1. Field of the Invention
The present invention relates to a head suspension of a hard disk drive incorporated in an information processor such as a personal computer.
2. Description of Related Art
A head suspension of a hard disk drive includes a load beam, a head supported with the load beam, and a slider attached to the head. The head suspension has a shock property that determines a lift of the slider from the surface of a hard disk when a shock is applied. The shock property of the head suspension is dependent on the weight of the load beam.
For example, a first head suspension has a load beam having a thickness (t) of 51 μm, a length (1L) of 7 mm, and a gram load of 2.5 gf that is applied by the load beam to a head, and a second head suspension has a load beam having a thickness (t) of 30 μm, a length (1L) of 5.5 mm, and a gram load of 2.5 gf. If a shock of 1 msec duration (1 msec in half wavelength) is applied to these head suspensions, a slider of the first head suspension lifts at an acceleration of 628 G and a slider of the second head suspension lifts at an acceleration of 1103 G.
To improve the shock property of a head suspension, a load beam of the head suspension must be thin and short and has a large gram load.
FIG. 14 is a plan view showing a head suspension 101 for a hard disk drive according to a related art. The head suspension 101 has a base plate 103, a load beam 105, and a flexure 107. The load beam 105 has a rigid part 109 and a resilient part 111. The rigid part 109 has a body 113 and a joint 115 that is attached to an end of the resilient part 111. Each side edge of the body 113 of the rigid part 109 is provided with a rail 117 that rises from the surface of the body 113.
FIG. 15 is a sectional view partly showing a hard disk drive in which the head suspension of FIG. 14 is installed. A carriage 119 has arms 121. To one of the arms 121, the base plate 103 of the head suspension 101 is fixed by, for example, swaging.
The carriage 119 is turned around a spindle 125 by a positioning motor 123 such as a voice-coil motor. The carriage 119 is turned around the spindle 125, to move a head 127 of the head suspension 101 to a target track on a hard disk 129.
When the disks 129 are rotated at high speed, the head 127 slightly rises from the surface of the disk 129 against the gram load of the head suspension 101.
To improve the shock property of the head suspension 101, the length (1L) of the load beam 105 is shortened and thinned, thereby reducing the weight of the load beam 105.
In practice, the arm 121 vibrates. Accordingly, the load beam 105 must be designed in consideration of the first bending frequency of the arm 121, i.e., the resonant frequency of the arm 121 in a first bending mode. The first bending frequency is hereinafter referred to as the “B1 frequency.” It is important to consider the B1 frequency of the arm 121 when determining a B1 frequency for the load beam 105.
FIGS. 16 to 18 are graphs showing a relationship between the B1 frequency and shock property of an arm installed in a 2.5-inch hard disk drive. Among the figures, FIG. 16 shows an acceleration representative of a shock applied to the hard disk drive at which a slider of the arm lifts, FIG. 17 shows a maximum acceleration occurring at the front end of the arm due to the applied shock, and FIG. 18 shows a maximum displacement of the arm due to the applied shock. In each of FIGS. 16 to 18, an abscissa indicates the B1 frequency of the arm. In each of FIGS. 16 and 17, an ordinate indicates an acceleration on the arm. In FIG. 18, an ordinate indicates a displacement of the arm. The magnitude of acceleration of the applied shock is 300 G in each case. The half-wavelength duration of the applied shock is 2 msec, 1 msec, or 0.4 msec.
It is understood in FIGS. 16 to 18 that the arm is substantially immovable against a shock of 2 msec or 1 msec duration if the B1 frequency of the arm is high (for example, 1.5 kHz) as indicated with curves 131A, 131B, 131C, 133A, 133B, and 133C. On the other hand, the arm differently acts against a shock of 0.4 msec duration, as indicated with curves 135A, 135B, and 135C.
This is because the arm conducts a large action with respect to a shock of 0.4 msec duration even if the B1 frequency of the arm is high.
A head suspension attached to such an arm must follow the arm action. If the load beam of a head suspension can follow the vibration of an arm, the slider of the head suspension will not lift from the surface of a disk.
Another consideration must be done for the off-track property of a head suspension. It is basically understood that the vertical rigidity (or stiffness) of a head suspension never acts in an off-track direction.
In practice, head suspensions involve a slight twist, and disks involve a slight inclination. Due to such twist and inclination, the vertical rigidity or B1 frequency of a head suspension influences the off-track property of the head suspension.
FIG. 19 is a graph showing the off-track property of a head suspension whose B1 frequency is 3.1 kHz. In FIG. 19, an abscissa indicates the frequency of an arm and an ordinate indicates off-track displacement. In the graph of FIG. 19, a curve depicted with a continuous line represents the off-track property of a head suspension measured on a 2.5-inch disk rotated at 5400 rpm and a curve depicted with a dotted line represents the off-track property of the head suspension measured on a 2.5-inch disk rotated at 7200 rpm.
In FIG. 19, the head suspension has a low B1 frequency of 3.1 kHz, and therefore, the bending mode of the head suspension overlaps the bending mode of the arm. As a result, an off-track phenomenon is observed at 3.0 kHz and at 3.3 kHz.
To avoid the off-track phenomenon, the B1 frequency of the load beam of the head suspension must be increased so that the bending mode of the head suspension will not overlap the bending mode of the arm.
To improve the B1 frequency of a load beam, forming the rail 117 along each side edge of the body 113 of the rigid part 109 as shown in FIG. 14 is effective.
When the head suspension is used for a 3.5-inch disk drive, forming the rail 117 entirely along each side edge of the body 113 of the rigid part 109 is not so demanded, because the 3.5-inch disk drive has a more intense need for a high sway frequency.
When the head suspension is used for a 2.5-inch disk drive, an improved shock property is acutely required. If no rail is formed along each side edge of the body 113 of the rigid part 109, the B1 frequency of the load beam is too low to satisfy the requirement.
FIGS. 20 and 21 show the structure of a head suspension according to a related art that can increase the B1 frequency of a load beam 105 to some extent. FIG. 20 is a plan view showing a first face of the head suspension and FIG. 21 is a perspective view partly showing the head suspension. In FIGS. 20 and 21, parts corresponding to those of FIG. 14 are represented with like reference numerals. The head suspension 101A of FIGS. 20 and 21 includes an arm 121A and a base 103A that are integral with each other.
The head suspension 101A has a rail 117 formed along each side edge of a body 113 of a rigid part 109, to improve the B1 frequency of the load beam 105.
The rigid part 109 has a joint 115 that is attached to a resilient part 111. The joint 115 has edges 137. When a plurality of rigid parts are cut from a plate material into individual rigid parts 109, the edges 137 of each rigid part 109 serve as parts that are cut from the adjacent edges 137. Due to this, it is impossible to extend the rail 117 along each edge 137 of the joint 115. This results in leaving a blank 139 between the rail 117 and the joint 115. The blank 139 which has no rails prevents the load beam 105 from increasing the B1 frequency thereof.
For the details of the above-mentioned related arts, U.S. Patent Publication No. 6,765,759 B2 and Japanese Unexamined Patent Application Publication No. 09-282624 can be referred to.